This invention, while not necessarily so limited, relates to wooden railroad crossties used to support rails on a railway roadbed and more particularly to wooden ties having cellular plastic inserts therein for retaining rail fastening devices.
In the conventional construction of railroads, a metallic tie plate carrying a rail is disposed upon a surface of a wooden tie to spread and distribute the load or weight transmitted to the tie from the rail supporting a passing train. This area of the tie beneath the tie plate is commonly referred to as the wear area because this is the area that tends to disintegrate sooner than the other areas of the tie. Conventionally, the tie plate and the rails are secured to the wooden tie by spikes driven through holes disposed near the lateral edges of the tie plate. These spikes secure the rail to the tie plate; and they likewise secure the tie plate to the wooden tie to restrict horizontal and vertical movements of the rail as a train passes over the rail.
Customarily, each of the two rails of a railroad track is canted inwardly by the tie plate being disposed at a slope of one unit of rise to 40 units of run to improve the load-bearing qualities and to help maintain the gauge (distance between the rails) of the rails particularly when a train passes. Because each rail is canted inwardly of the track, the passage of train wheels on the track tends to cause a slight horizontal and vertical movement of the rail to occur. These movements simulate a wave. Such combination of vertical and horizontal motion tends to effect a rocking movement of the tie plate on the tie which movement, in turn, causes loosening of the spikes driven through the tie plate and into the tie. Therefore, the spikes have to be tightened within predetermined intervals. After a certain time, however, such a tightening procedure is no longer possible, because the wood in the vicinity of spike holes on account of moisture, biological influences, stresses and the like, has become so deteriorated and disintegrated that the spikes no longer have a sufficient hold therein. Such a deteriorated condition of the tie is known in the art as "spike-kill." The condition is further aggravated by a phenomenon known in the art as "plate cutting" wherein the rocking movement of the tie plate on the tie causes an indentation in the tie, i.e., the cutting or wearing of the wooden tie in the wear area.
The process of "spike-kill" is accelerated by a number of other factors. For instance, dust and abrasive particles from the roadbed are trapped in the enlarged spike holes. The rocking movement of the spikes under the load and vibration of passing trains literally grind the abrasive particles in the spike holes into the surrounding tie destroying the supporting characteristics of the wood fibers and further enlarging the spike holes. In recent years, the problem of "spike-kill" has further been aggravated by the increased loading and the faster speed of travel of rail cars, which have significantly increased the cyclic impact loading of the tie through the rail and tie plate.
The "spike-killed" ties have often been replaced at a considerable expense of time, labor and materials. To salvage the "spike-killed" ties that are not replaced, it has been the practice to bore out the worn spike holes and to set in wooden dowels, or to fill such holes with epoxy resin. Wooden dowels are disadvantageous because they are usually cut lengthwise of the grain and cause their end grain to be exposed to environmental water penetration and are subject to splitting when a spike is driven into the dowel. Resin filled holes are disadvantageous because the resin mass is different from the surrounding wood and a spike cannot be driven into the resin. It is also known to repair the "spike-killed" tie by closing the worn spike holes with wooden dowels and to slidably displace the tie plates away from their old position and then to respike these plates to the tie in the new position. This type of repair is also very time consuming and expensive and can only be used for a limited number of times.
An object of this invention is to provide a new and advantageous crosstie for use in conventional railroad track systems, particularly to support and secure rails on a railway roadbed composed of particulate ballast such as crushed rock.
Another object is to provide such crossties which are more durable and more resistant to "spike-kill" than wooden ties but which have at least comparable holding power to retain the spikes in position.
Yet another object is to provide a method of upgrading or repairing "spike-killed" wooden ties in service without major modification of the track.
Other objects and advantages of the invention will become apparent in the following description.